Filter cake washing



June 15, 1937. v Q E T I 2,083,578

FILTER CAKE WASH ING Filed Sept. 25, 1954 [72229212 07- Oscar L.R0berls his Alforney produced (in. the,

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'Ihe pres entinventio elatestoa inethodffor filtering or separating solids -from 1iq 1iids and '1. grepartiqu lv toithe washing For extraction of I Y MY, F Q 5 articularly applicable to the. removal of liquid constituents from press 11 makes,

e n fi ii n s therefrom. 1:

a for example; the removal Z In'the separation of-.-pfaramn we from-hydrocarbon oils, such'as petroleumzlubricatlng oils, it

u is common practice to; filter. thezcoil-wax mix- 1 vtux-e under pressure, with or withoutdilut'ionfwlth 151avlowyiscosity solventuThe wax-'cake vo'btalhed $5 1 ltr tion-P ce s.usuallyiconteinsconsidiv-Submerged liquid and that the a it o erable' quantitiespf oil,- 1'.;e., on theaorder 01-50% I or mor by weightofthe;cakekJ -someinstances Y the cake may be washedgwith.asolvenfliquid,

go preferably a liquidcompletely misclble with the .oil corlt'ent of the cake maybe reduced; However, l lij genera; :the: W8 $l fi1{1g*-f- -1 the press cake is, not L complete',' theoil ontent of thelc'ake :beingtof the The practice of washingwax cakes is-confined p i ma rilyr to filters}; 19f Q the suction; deaf in hich' the; re hmlh-upqonQthecuter surface" of th ressjleaves; In; accordancewith the :sufiicle'nt gas pressure V 351s maintained; pnthe I cake toy-prevent: the same [frombreakingdoose,anddropping from theilea'ves. In many "instances sumcient gas kpressurelsapplied j' to, the press? cake; to force a portion-f, ft h 011 contaihed therein=comp1etelythrough and '40 out jot i said cake. When the unfiltered-slurry has been, ,ren1oved from the ;.press1,;casing, wash solvent is pas ed 1 ii'xto I the gcasing,v thereby disv 'lgasf and 'competely;suh;nerg1ng;;thefla h s lvent E -1 he' through thecakeg und'er substantial press.ure, ,and-

" 'ntained therein; is thus it h orlr washedj cake is usually upwardsnoff2'5 hyweigmh The high" all content, qt ,jthe l press 5 ca k eg may -be a1 corp i ration of Pennsylvania.

Application"September g5, -l934,i$erial er a cake ottheproper size has been-deposited t non-uniformity generally results fromthe uni eve'n "size" an distribution offjthe'wax crystals upon the-pressleavesvand is further aggravated by thjfemplcy cake in'-place or t'o "force a {portion of the con- "'tained oil rr'qmm .calgie. I haveffound that if t 'cf gas pressure tohold the the unfll'tred is drained from' the press "casing andthei cake is subjected to gas pressure} cracks or channels-will fdevelopfwithin the, "cake, thereby?ipermlttlngpassage of 'wash solvent throughthefpath" of 'least'resistance, i, c l-"the icha nnels, upon "subsequent washing of" the" cake 'with'a'solvent-liquid.

-. In order to" overcome manner that' the cake is at an times completely washsolventrequired for a thorough washingfof t Briefly; method comprises 'passin'g a wax tslurryyprepared froma wax-containing oil stock,-

either as such'or in gdilutlohina -'suitabljef slol-.

n edn-thicknessfupon the press leave'sand then In. employing fakswash. solvent of lowerl speciflc gravity than that or theqliquid portion of the j unfiltered wax, slurry; such wash solvent is pretwith theysll 'ri'sp 0nathe pther handgif'th wash solvent a .specific, gravity greater :than "that r this dimemty iptosase .yto effectwashlng of the wax' cake in such a (v m -1mm eapfilteriipress of the "stationary .or v

rotary leaf. type;- buildingmp j'awax cake o'fderel ably introduced. above thealiquid level'of' the slurry in the casi-ng,fa.n'ddisplacement of the let- 1 ter lfrorn theg casingais :effectedl downwardly without (substantial; internuxingof the wash "solvent oi thdllquidportion of; the unfilteredslurryfsuch wa'sh solvent is preferably introduced at the bot} "jtom'of the vpressqasing, and the slurry is dispIacedupWardIyand out of the casing-without .substantial'intermixing. p i v v Fora lurthen u derstanding of my invention, I reference ls made. to; the. accompanying drawing which illustrates, in zrosssectio l,:apparatus sui table for carrying on my:process. v. t

" clean 2 having perforated.j sidenplates 3 covered with n, 1

filtering medium suchfas canvas 4. The upper end of cell 2 is connected to the filtrate outlet pipe 5 controlledby valve The filter casing 1 controlled by valve 8, wash solvent inlet pipes 9 and I I controlled by valves I0 and I2 respectively, slurry inlet pipe I3 controlled by valve Hand slurry discharge pipe I5 controlled by valve I I5.

Exemplary of operation, in accordance with my invention, is the following: the filter casing I is filled with wax slurry introduced through pipe I3, valves 6, 8, land I2 being closed and valve I6 being open as a vent. When the casing I has been filled, .valve 6 is opened and valve I8 closed, suction is. then applied to filtrate outlet pipe 5, and the solid constituent'of the slurry,

i. e., the wax is deposited upon the canvas covered" plates 3, while the oil or oil solution passes through the perforated plates to the interior of the cell 2 and is withdrawnthrough outlet pipe casing I.

When the wax cakes I! have been built up to the desired thickness, the slurry supply is shut off by means of valve I4' and thevalve 6 of f1]- trate outlet pipe 5 is preferably adjusted to permit only a very smallfiowf therethrough. The

suming, in this instance, that the specific gravity of the wash solvent is lower than that .of the liquid portion of the unfiltered slurry remaining The displacement'of the slurrybythe wash solvent'is effected in such a manner that a substantially uniform or undisturbed interfacels mainftained' between the two liquids and the wax this operation.

cakes are completely submerged in liquid during differential pressure ismaintained between the place. For purposes of illustration this interface .is indicated bythe line I8.

When substantially all of the unfiltered slurry f has been displaced from ,thefilter casing I, valve therefrom and such wash solvent 'is withdrawn the cakes to break the same'loose from the canvas, and the disintegrated wax may then be withdrawnfrom the casing through pipe I.

I If the specific gravity of the wash-solvent employed is greater than" that of the wax slurry, such solvent would be introduced at thebottom of the filter casing I by means of pipe II. Uniform displacement of the unfiltered slurry would take place upwardly, such slurry being Withdrawn from the top of the casing I through pipe I5.-. The washing operation would then be car-- ried on substantially as above described.

While I have illustrated my invention in connection with a-filter unit provided with only one stationary cell, I do not intend to'limit myself step of cake-washing is then commenced. As-

At the same time a sufficient drawn formation of cracks or channels within the cake which would permit by-passing of the wash solvent through portions of the cake. Furthermore, by displacing the unfiltered slurry from the press casing without substantial admixing with the ,Wash solvent, I prevent contamination of the latter with slurry and I am therefore able to effect adegree-of washing with a small quantity of solvent as heretofore has been obtained only with I much larger quantities of the solvent when same 5, f h sl y ing n in ly pp t fiwas permittedito become mixed with the slurry.

For example, the quantity of unfiltered wax v 45 barrels. In order .to obtain a-thorough washing of the wax cake Withthe minimum quantity of washsolvent, such unfiltered slurry must be removed from the press casing witho1i'tsubstantial admixture thereof with the wash solvent being introduced, and without permitting the cake to emerge from the liquid. I It will be understood that when'rny invention is appliedtoa movable leaf filter, as for example, of the rotary leaf type, the leaves of such filter, preferably, are kept stationaryduring the displacement of slurry by wash liquid. j

My process is not confined to' the employment of any particular diluent or wash solvent, but may be applied in any filter pressing operation involving the separation of oil from wax, and particularly when solvents such as propane, butane, surface of the wax cake I! and the interior of cell 2 to hold the wax cake undisturbed and in ethylene .dichloride, acetone-benzol and similar agents are employed. I v

For brevity,'in the appended claims, the term wash liquid is to be'understood to comprehend a liquid which 'at the-temperature of separation,

is miscible with the liquid constituents, but relativelyimmiscible with the solid-constituents of the mixture to be separated. WhatIclaimis; I u

1. In a process for separating solid wax from a mixture comprising liquid oil and'solid wax, the steps which comprise continuously passing" said mixture into a filtering zone, passing oil from said filtering zone through "a filtermedium while depositing thereon a 'filter cake of wax containing oil, discontinuing the pas'sage of said mixture into the filtering 'zone, withdrawingj from said zone.

the unfiltered mixture surrounding said wax cake,

introducing into said zone a Wash liquid of a specific gravity different from that of said mixture at a locus such that the liquid of greater specific gravity underlies that of lesser specific gravity and at a rate corresponding substantially tothe rate of withdrawal of the unfiltered mixture, thereby to displace said unfiltered mixture and to maintain 'a substantially uniform interface between said wash liquid and said unfiltered mixture, said wax cakejbeing maintained substantially completely submerged in liquid throughout the displacement operation, and passing at least a portion of said wash liquid through said filter cake to wash therefrom the oil containedtherein. 2. In a process for separating solid wax from a mixture comprising liquid oil and solid wax, the steps which comprise continuously passing said mixture into a filtering zone, passing oil from said filtering zone through a filter medium while depositing thereon a filter cake of wax containing oil, discontinuing the passage of said mixture into the filtering zone, withdrawing from said zone the unfiltered mixture surrounding said wax cake, introducing into said zone a wash liquid of a specific gravity different from that of said mixture at a locus such that the liquid of greater specific gravity underlies that of lesser specific gravity and at a rate corresponding substantially to the rate of withdrawal of the unfiltered mixture, thereby to displace said unfiltered mixture and to maintain a substantially uniform interface between said wash liquid and said unfiltered mixture, said wax cake being maintained substantially completely submerged in liquid throughout the displacement operation, and, upon substantially complete removal of said unfiltered mixture from the filtering zone, passing at least a portion of said wash liquid through said'filter cake to wash therefrom the oil contained therein.

3. In a process for separating solid wax from a mixture comprising liquid oil and solid wax, the

steps which comprise continuously passing said mixture into a filtering zone, passing oil from said filtering zone through a filter medium while depositing thereon a filter cake of wax containing oil, discontinuing the passage of said mixture into the filtering zone, throttling the passage of liquid through the filter medium, withdrawing from said zone the unfiltered mixture surrounding said wax cake, introducing into said zone a wash liquid of a specific gravity different from that of said mixture at a locus such that the liquid of greater specific gravity underlies that of lesser specific gravity and at a rate corresponding substantially to the rate of withdrawal of the unfiltered mixture, thereby to displace said unfiltered mixture and to maintain a substantially uniform interface between said wash liquid and said unfiltered mixture, said wax cake being maintained substantially completely submerged in liquid throughout the displacement operation, and subsequently passing .at least a portion of said wash liquid through said filter cake to wash therefrom the oil contained therein.

OSCAR L. ROBERTS. 

